a) Field of the Invention
The invention is directed to a radiation source for generating extreme ultraviolet (EUV) radiation, particularly for photolithography exposure processes. It is preferably applied in the semiconductor industry for the fabrication of semiconductor chips with structure widths of less than 50 nm.
b) Description of the Related Art
Gas discharge plasmas and laser-induced plasmas are known as emitters of EUV radiation. Different applications of this radiation are currently under examination, e.g., lithography, microscopy, reflectometry and surface analyses. Intensive, dependable radiation sources are required for all of these different applications.
EUV radiation sources will be required in the future primarily in the semiconductor industry for exposing very small structures in lithography processes in order to be able to produce structure widths of less than 50 nm with very good reproducibility with a high throughput of semiconductor wafers.
At the present time, EUV radiation sources are built as prototypes. The individual structural component parts are brought into line with one another predominantly in a function-oriented manner. It is difficult to exchange components in a source that is conceived in this way and compatibility with other applications is impossible. However, there is also a demand for maintaining stable radiation characteristics throughout the duration of operation as well as for inexpensive exchange of defective or worn components.
Similar problems are addressed in U.S. Pat. No. 6,018,537 for reliable series production of excimer lasers. In this case, a 10-mJ-F2 laser with a pulse rate of 1-2 kHz is constructed in such a way that determined control modules are associated with the units of the radiation source which essentially determine the radiation output and repetition rate of the laser. Apart from the general task of controlling or regulating certain influencing variables of the laser, these control modules can not be adopted for the complicated control functions of a EUV radiation source.